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SGUL - Physiology 1 > Coordinated Responses of The CVS * > Flashcards

Coordinated Responses of The CVS * Flashcards

1
Q

What is orthostasis?

A

Standing up

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2
Q

What are the effects of orthostasis on the blood flow to the brain?

A
  • CVS experiences changes due to gravity
  • Postural hypotension causing lack of blood flow to the brain due to fall in blood pressure
  • In extreme cases, fainting
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3
Q

How does the body counteract postural hypotension caused by orthostasis?

A
  • Fall in BP recovers due to homeostatic mechanisms such as baroreflex
  • Increases heart rate, force of contraction and TPR
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4
Q

Describe the effects of orthostasis on blood pressure on different parts of the body.

A
  • Blood pressure is lowest at the head and highest at the feet.
  • REASON: force of gravity pulling blood down towards the feet
  • More blood pooling at the feet
  • Applies a greater hydrostatic pressure on the vascular wall
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5
Q

How is Bernoulli’s law used to counteract the pooling of blood at the feet during orthostasis?

A
  • Increase in potential energy (from heart to feet)
  • Increase in kinetic energy of ejected blood
  • Increases blood flow
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6
Q

Why can orthostasis sometimes cause fainting? PART 1

A
  • Blood starts to pool in the legs under the force of gravity
  • CVP decreases
  • Less blood returns to the heart so EDV decreases
  • Less filling so less stretch in the heart
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7
Q

Why can orthostasis sometimes cause fainting? PART 2

A
  • Force of contraction would be weaker (Starling’s law)
  • Decrease in stroke volume
  • Decrease in cardiac output
  • Poor perfusion of the brain causing fainting
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8
Q

How does lying down/fainting counteract hypotension? PART 1

A
  • Blood is evenly distributed in the veins
  • CVP increases
  • Greater filling
  • EDV increases
  • Greater stretching of vascular muscles.
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9
Q

How does lying down/fainting counteract hypotension? PART 2

A
  • Increased force of contraction
  • Increased stroke volume
    -Increased cardiac output
  • Better perfusion of the brain
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10
Q

How do alpha-adrenergic blockers make postural hypotension worse?

A
  • Reduce vascular tone
  • Inhibit the body’s ability to respond to an increase in vascular tone
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11
Q

How can impairment of varicose veins make postural hypotension worse?

A

Impairs venous return as more blood will pool in the veins

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12
Q

How can a lack of skeletal muscle activity make postural hypotension worse?

A
  • Occurs due to paralysis or forced inactivity (e.g. long term bed rest)
  • Muscles required to help pump blood into the heart
  • Inactivity reduces the amount of blood leading to the heart
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13
Q

How can a reduction in circulating volume make postural hypotension worse?

A

Reduces preload and so baroreceptors are not able to respond to changes (e.g. haemorrhage)

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14
Q

How can increased core body temperatures make postural hypotension worse?

A
  • Peripheral vasodilation
  • Reduces the amount of blood going to the heart
  • Less stroke volume and cardiac output
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15
Q

What are the initial effects of microgravity (space) on the CVS? PART 1

A
  • Blood returns to the heart
  • Increases atrial and ventricular volume
  • Increased cardiac output.
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16
Q

What are the initial effects of microgravity (space) on the CVS? PART 2

A
  • Sensed by cardiac mechanoreceptors which reduce sympathetic activity.
  • Reduces ADH and increases ANP which increases GFR and reduces RAAS.
  • Overall reduction in blood volume
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17
Q

What are the long term effects of microgravity on the CVS?

A
  • Lower blood volume as there is reduced stress on the heart.
  • Causes the heart to reduce in muscle mass
  • Causes BP to drop.
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18
Q

Some astronauts suffer from postural hypotension after returning to Earth from space. Suggest why.

A
  • Smaller blood volume and smaller heart due to long-term effects of being in space (microgravity).
  • Baroreceptors cannot compensate for this
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19
Q

What does the body aim to do when exercising?

A

Mechanisms occur that increase blood supply to exercising muscle

20
Q

What causes the changes in cardiovascular activity in the body during exercise?

A
  • Central command in the brain in response to stimuli (e.g. anticipation of exercise)
  • Feedback from muscles through mechanoreceptors and metaboreceptors
  • This affects sympathetic activity and vagus inhibition
21
Q

What changes do we see in the CVS during exercise? PART 1

A

Increase lung oxygen uptake
- Oxygen is transported around the body to supply exercising muscles.
- Requires an increased HR and increased force of contraction

22
Q

What changes do we see in the CVS during exercise? PART 2

A

Constant control of BP
By controlling BP, can increase cardiac output and protect the heart from excessive damage caused by increased BP (arising from increased HR)

23
Q

What changes do we see in the CVS during exercise? PART 3

A

Co-ordinated dilation/constriction of vascular beds
- Allows selective targeting of areas to which oxygen is delivered i.e muscles

24
Q

How is oxygen uptake into the lungs increased during exercise? PART 1

A
  • Increase in heart rate and stroke volume
  • Blood pumped around the body at a faster rate
  • Oxygen gets used up by respiring tissue more quickly
25
Q

How is oxygen uptake into the lungs increased during exercise? PART 2

A
  • Increase difference in arteriovenous oxygen difference.
  • The bigger the difference in oxygen concentration in the arteries and veins the bigger the concentration gradient
  • Faster diffusion.
26
Q

How does arterio-venous oxygen difference change with increasing intensity of exercise? (REFER TO CURVE ON SLIDES)

A
  • During light exercise the arterio-venous oxygen difference is low
  • From light to moderate intensity this oxygen difference increases very steeply
  • From moderate to heavy the curve is now less steep but still continues to rise
  • At heavy exercise the curve starts to plateau
27
Q

How does cardiac output change with increasing intensities of exercise?

A
  • During light exercise - very low cardiac output.
  • From light to medium intensity - small increase in cardiac output
  • From medium to heavy - greater increase in cardiac output
  • Heavy exercise - cardiac output increases dramatically
28
Q

How does stroke volume change with increasing intensities of exercise? PART 1

A
  • During light exercise - very low stroke volume
  • From light to medium intensity - large increase in stroke volume due to Starling’s law (increased stretching)
29
Q

How does stroke volume change with increasing intensities of exercise? PART 2

A
  • From medium to heavy - smaller increase in stroke volume as there is a decreased cardiac output due to reaching elastic limit of Starling’s law
  • Heavy exercise the stroke volume starts to decrease
30
Q

How does heart rate change with increasing intensities of exercise?

A
  • During light exercise - very low HR
  • From light to medium intensity - small increase in HR
  • From medium to heavy - greater increase in HR
  • Heavy exercise - HR increases dramatically
31
Q

What is fast heart rate called?

A

Tachycardia

32
Q

How is tachycardia achieved?

A
  • Caused by the brain central command
  • Decrease in the signal down the vagus nerve to the SA and AV nodes
  • Increase in sympathetic activity to the SA and AV nodes
  • Causes the heart rate to increase
33
Q

How is stroke volume increased using EDV?

A
  • High EDV so filling pressure is high
  • Increased sympathetic activity and other systems e.g the calf muscle pump causes venoconstriction
  • Increases CVP
  • Starling’s law increases preload
34
Q

How does faster ejection lead to a greater stroke volume?

A
  • Increased sympathetic activation of β-1 receptors
  • Inotropic Ca2+ to increase the speed of ejection
35
Q

How is stroke volume increased using ESV?

A
  • Decreased end-systolic volume so increased ejection
  • Increased contractility by sympathetic activation of β-1 receptors
  • Increases stretching
36
Q

What are the effects of an increase in cardiac output during exercise?

A
  • Overall decrease in TPR
  • Blood pressure doesn’t increase by much
  • Systolic and diastolic volumes increase
  • Stroke volume and filling are greater
37
Q

What is compensatory vasoconstriction?

A
  • The vasoconstriction/blocking of blood supply to less active parts of the body during exercise i.e
  • Prevents hypotension as exercise causes decreased TPR so prevents the BP from getting too high/low
38
Q

What are metaboreceptors?

A

Small chemosensitive sensory fibres in skeletal muscle

39
Q

What are metaboreceptors stimulated by

A

Stimulated by K+, H+ and lactate (which increase in exercising muscle)

40
Q

What reflex actions do metaboreceptors cause?

A
  • Tachycardia due to increased sympathetic activity
  • Increased blood pressure
  • Pressor response to exercise
41
Q

What is the reflex response to orthostasis? PART 1

A
  • Less stimulation (unloading of baroreceptors)
  • Lower afferent fibre activity
  • Signal goes to NTS
  • Switches off inhibitory nerves that go from CVLM to the RVLM.
  • Results in RVLM being more active sending efferent signals to heart and arterioles.
42
Q

What is the reflex response to orthostasis? PART 2

A
  • Increased sympathetic drive to SA node and increased HR.
  • Myocardium increased contractility
  • Vasoconstriction (arterioles, veins) increases TPR.
  • Less vagal parasympathetic activity to SA node – overall increase in blood pressure.
43
Q

What is dynamic exercise associated with?

A

Constantly shortening and of different muscle groups– associated with a lower BP, lower sympathetic tone
- Involves ‘lower loaded’ exercise

44
Q

What is static exercise associated with?

A

One specific muscle group is being worked without constant movement – associated with higher BP and metabolic hyperaemia

45
Q

Describe the two different ways vasodilation occurs.

A
  • Fall in local resistance due to metabolic hyperaemia
  • Local sympathetic response can also occur - β2-mediated vasodilation via circulating adrenaline.
  • β2 receptor expression high in skeletal muscle and coronary artery.
46
Q

When are metaboreceptors particularly important?

A

Isometric exercise

47
Q

hat is the effect of an increase in BP caused by metaboreceptors?

A
  • Raised BP maintains blood flow to contracted muscle
  • Contracted muscle also supplied by dilated resistance vessels due to metabolism - selective metabolic hyperaemia.

SGUL - Physiology 1 (68 decks)

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